Patent Document 1 describes a plasma processing method. In this plasma processing method, a MRAM device is manufactured by processing a multilayered object including a magnetic tunnel junction (MTJ) in which an insulating layer is interposed between a lower magnetic layer and an upper magnetic layer. Herein, as a material of the insulating layer, Al2O3 is used. The lower magnetic layer has a fixed magnetization direction, and a magnetization direction of the upper magnetic layer is changed by an external magnetic field. To be specific, according to the method described in Patent Document 1, the MRAM device is manufactured by (a) forming a first mask on an upper electrode layer, (b) plasma-etching the upper electrode layer, the upper magnetic layer, and the insulating layer, (c) removing the first mask, (d) forming a second mask on the upper electrode layer, and (e) etching a lower electrode layer.    Patent Document 1: Specification of U.S. Patent Laid-open Publication No. 2004/0137749
In an apparatus described in Patent Document 1, when the multilayered object is etched, a residue containing a conductive material may be deposited on a side wall of the insulating layer. If the residue is deposited on the side wall of the insulating layer, a leak current may be generated at the MTJ and characteristics of the MRAM device may be deteriorated. In order to solve such a problem, it is considered that the etching process is stopped for the moment on a top surface of the insulating layer to suppress the residue from being deposited on the side wall of the insulating layer. In this case, it is necessary to increase etching selectivity between the magnetic layer and the insulating layer.
Meanwhile, it is known that if MgO is employed as a material of the insulating layer of the MTJ device, a high MR ratio can be achieved. However, since MgO is a new material for the insulating layer of the MTJ device, there have not been known etching conditions in which high selectivity between a magnetic layer and an insulating layer made of MgO can be obtained.
Further, in order to etch a magnetic layer, a metal mask needs to be formed on the magnetic layer by the etching process or the like. However, when the metal mask is formed on the magnetic layer, a top surface (surface) of the magnetic layer may be modified and a modified layer different from the magnetic layer may be formed. There have not been known conditions for etching a magnetic layer including this modified layer.
For this reason, in the corresponding technical field, there have been required a plasma processing method and a plasma processing apparatus in which an etching of a magnetic layer can be stopped for the moment on a top surface of an insulating layer made of MgO to suppress a leak current from occurring and to improve characteristics of a MRAM device.